1. Field of the Invention
The present invention relates to an asphalt modifier composition comprising a rubber-base modifier and/or a resin-base modifier, and a phosphorus compound, and an asphalt composition prepared by using the same. More particularly, the present invention relates to an asphalt modifier composition in which the solubility of the rubber-base modifier and/or the resin-base modifier contained therein as the main component(s) in asphalt is excellent when mixed with asphalt, and an asphalt composition prepared by using the same, which is excellent in adhesion to an aggregate, and which, when used for executing a pavement, can markedly reduce the formation of rutting and wearing of the pavement and can prolong the service life of the pavement.
2. Description of the Related Art
An asphalt composition for paving comprises asphalt and, in addition, various additives for improving the properties such as weather resistance and temperature dependence of the asphalt. Such the asphalt composition is used for paving in places where conventional petroleum asphalt, when used alone, has no satisfactory function or places where the long-term service life and durability of the pavement are required. Examples of such additives include rubber-base modifiers, such as natural rubber, styrene-butadiene rubber and chloroprene rubber, and resin-base modifiers, such as polyethylene, polypropylene, ethylene-vinyl acetate copolymer, ethylene-ethyl acrylate copolymer and polyesters. They are used alone or as a mixture of two or more of them.
Since, however, these modifiers have poor compatibility with asphalt, the following problems arise.
(1) In order to prepare a homogeneous asphalt composition, a mixture of an asphalt with the modifier must be agitated with heating at a high temperature for a long period of time. As the result, the problem of denaturations of the modifier and the asphalt arises, and the resultant asphalt composition has such disadvantages that designed dynamic stability and toughness tenacity cannot be provided and that a pavement executed by using the asphalt composition suffers from significant wearing. Further, the asphalt is denatured, which deteriorates the dispersibility of asphaltene (n-pentane insolubles) contained in the asphalt and the homogeneity of the asphalt. Thus, a problem of lowering the adhesion of the asphalt to an aggregate arises as well. PA0 (2) The modifier which has been homogeneously dispersed in the asphalt agglomerates during storage under heating, thus causing the modifier to be separated from the asphalt. For example, a styrene-butadiene rubber which is one member of modifiers has a lower specific gravity (about 0.93/15.degree. C.) than the asphalt (specific gravity: about 1.04/15.degree. C.). Therefore, when the separation of the modifier from the asphalt has occurred during storage of the asphalt composition in a storage tank under heating, the modifier is unevenly distributed. As the result, in the upper part of the asphalt composition, the modifier (styrene-butadiene rubber) becomes rich, while in the lower part thereof, the modifier becomes poor. Thus, the asphalt composition includes a part not exhibiting designed various properties. When an asphalt composition which is poor in the modifier content is used for paving, the resultant pavement has very poor rutting resistance and wearing resistance.
In order to solve the above problem, that is, the problem of the separation of the modifier from the asphalt at high temperatures, Japanese Patent Publication-A No. 6-329919 proposes a process comprising using, together with an asphalt, an ester prepared by reacting a copolymer prepared from an ethylenically unsaturated carboxylic acid and an aromatic vinyl compound with a hydroxyl group-containing compound, or a salt of the ester, and Japanese Patent Publication-A No. 7-157665 discloses the utilization of an asphalt modifier comprising an oil-soluble polymer having both an acid group and a basic group.
The adoption of these methods results in somewhat improvement of the properties of the asphalt composition. However, a further improvement in the dispersibility of the modifier, when the asphalt composition is allowed to stand without agitation for a long period of time, has been desired in the art.
Further, it is required that the asphalt is less likely to be stripped from the aggregate for improving the properties of a pavement executed by using an asphalt composition. For this reason, in order to improve the adhesion of the asphalt to the aggregate, Japanese Patent Publication-A No. 60-188462 proposes the addition of a specific acid organophosphorus compound to an asphalt, while Japanese Patent Publication-A No. 6-192579 proposes the use of polypropylene or polyethylene modified with maleic anhydride as the modifier.
In recent years, there is a fear of the deterioration in the quality of asphalt, while there is a fear of a good-quality aggregate for paving being exhausted. Therefore, a further improvement in the adhesion of the asphalt to the aggregate has been desired in the art.